any type in callback parameter

[NN---]

Is it intended behavior ?

function x(f: (g: number) => void): void { f(1); }

x(function (d) {
   // d is number
});

Adding parentheses around the function makes 'd' to be any type:

function x(f: (g: number) => void): void { f(1); }

x((function (d) {
  // d is any
}));

[DanielRosenwasser]

Yes; parentheses "turns off" contextual typing.

It is definitely something we're aware tends to be a problem for many, and #920 moves to give you the behavior you expect.

[NN---]

The problem is that I have code like this:

f((function(d){
}).bind(abc));

I do need parentheses here and then I lose type safety:(

[CyrusNajmabadi]

@nn there is nothing we can do in that case. Contextual typing wouldn't apply anyways as the expression being passed to 'f' is the '.bind' call, not the function expression.

[NN---]

I see but in the function itself I expect parameter "d" to be a number and get an appropriate code completion.
The real case is some class and it is more complicated.

Also there is a workaround specifying type explicitly :

x((function (d:number){
}).bind(abc));

I really would like to make the compiler inferring the type instead of writing by myself.

Thanks .

[DanielRosenwasser]

I see - so you want contextual typing to apply simply for the sake of editing prior to the call to bind. That's an interesting scenario, but keep in mind that even with the relevant change, if you ever went back to change your function, your parameter would implicitly be typed as any.

[NN---]

It is pretty annoying but I don't know how to solve it .
I think VS integration could propose a type hint in this case. I mean it can show a popup suggesting adding explicit types to callback function parameters until there will be a perfect solution.

[DanielRosenwasser]

As a note, compiling with the --noImplicitAny flag will appropriately hint that off to you.

[NN---]

Thanks.
I didn't notice that it is off by default.

In any case I would like to see some solution for this.
It is very common in JS to use 'bind' function and losing type safety is not a good option.

[danquirk]

See #212

[DanielRosenwasser]

Additionally, we have contextual typing on parenthesized expressions in master now.